Vacuum pump and heating device therefor

ABSTRACT

A vacuum pump suitable for prolonging the life of a heating means used as a measure to prevent product deposition in the vacuum pump, and a heating device for the vacuum pump. A vacuum pump that exhausts gas by rotation of a rotating body has an exhaust flow path for exhausting the gas, and a heating means for heating the exhaust flow path, wherein the heating means has a plurality of resistance heating elements connected in parallel to a pair of wiring lines. The heating means has a current measuring means for measuring a sum of values of currents flowing through the plurality of resistance heating elements, a determination means for determining failure conditions of the plurality of resistance heating elements on the basis of a measured value obtained by the current measuring means, and an output means for outputting the failure conditions determined by the determination means.

This application is a U.S. national phase application under 37 U.S.C. §371 of international application number PCT/JP2018/019824 filed on May23, 2018, which claims the benefit of priority to JP application number2017-106108 filed May 30, 2017. The entire contents of each ofinternational application number PCT/JP2018/019824 and JP applicationnumber 2017-106108 are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a vacuum pump used as a gas exhaustmeans for a process chamber or other vacuum chamber in a semiconductormanufacturing apparatus, a flat panel display manufacturing apparatus,and a solar panel manufacturing apparatus, and a heating device for thisvacuum pump. The present disclosure is especially suitable forprolonging the life of a heating means used as a measure to preventproduct deposition in a vacuum pump.

BACKGROUND

As this type of vacuum pump, the vacuum pump described in, for example,Japanese Patent Application Laid-open No. 2015-31153 has conventionallybeen known. The vacuum pump disclosed in Japanese Patent ApplicationLaid-open No. 2015-31153 includes a rotating body comprising a rotor (4)and rotor blades (6), wherein gas molecules are transferred from aninlet port to an outlet port (2) by means of the interaction betweenrotation of the rotating body and a stator member, that is, theinteraction between the rotor blades (6) and stator blades (7), as wellas the interaction between an outer peripheral surface of the rotor (4)and a thread groove stator (8), thereby exhausting a process gas used ina semiconductor manufacturing apparatus.

Incidentally, sublimable gas contained in the above-mentioned processgas becomes a gas or a solid due to the relationship between thetemperature and partial pressure of the gas and easily becomessolidified under a low-temperature environment or a high-partialpressure environment. Therefore, in the vacuum pump disclosed inJapanese Patent Application Laid-open No. 2015-31153, of the entireexhaust flow path for exhausting the gas, a part where the sublimablegas easily becomes solidified, that is, the vicinity of the exit of theexhaust flow path (R2) configured by the outer peripheral surface of therotor (4) and the thread groove stator (8), is intensively heated by aplurality of resistance heating elements (13).

However, in this conventional vacuum pump, a specific configuration ofthe resistance heating elements (13) used for such heating specificallyadopts an electric circuit configuration in which a plurality ofresistance heating elements RE are connected in series as shown in FIG.6. A problem with this configuration, therefore, is that in a case offailure such as disconnection in any of the resistance heating elementsRE, for example, currents no longer flow through all the resistanceheating elements RE, and consequently the operation of the heating meanshaving the plurality of resistance heating elements RE (the operation ofheating the vicinity of the exit of the exhaust flow path using theresistance heating elements RE) completely stops or shuts down,resulting in a shortened life of the heating means.

In such a case where the operation of the heating means completely stopsor shuts down, the sublimable gas easily becomes solidified in thevicinity of the exit of the exhaust flow path (R2) and the resultantsolid product (solidified sublimable gas) accumulates, lowering theexhaust efficiency and making it difficult to keep the exhaustperformance of the vacuum pump. Consequently, the operation of a deviceto be vacuumed by the vacuum pump or, for example, a process apparatusin a semiconductor manufacturing apparatus, may need to be stoppedimmediately.

In the foregoing description, the reference numerals in the parenthesisrepresent reference numerals used in Japanese Patent ApplicationLaid-open No. 2015-31153.

SUMMARY

The present disclosure was contrived in order to solve the foregoingproblems, and an object thereof is to provide a vacuum pump suitable forprolonging the life of a heating means used as a measure to preventproduct deposition in the vacuum pump, and a heating device for thevacuum pump.

In order to achieve this object, the present disclosure provides avacuum pump that exhausts gas by rotation of a rotating body, the vacuumpump comprising: an exhaust flow path for exhausting the gas; and aheating means for heating the exhaust flow path, wherein the heatingmeans includes a plurality of resistance heating elements connected inparallel to a pair of wiring lines.

The present disclosure may also include a current measuring means formeasuring a sum of values of currents flowing through the plurality ofresistance heating elements, and a determination means for determiningfailure conditions of the plurality of resistance heating elements onthe basis of a measured value obtained by the current measuring means.

The present disclosure may also include an output means for outputtingthe failure conditions determined by the determination means.

In the present disclosure, the failure conditions may be the number offaulty resistance heating elements out of the plurality of resistanceheating elements.

In the present disclosure, the pair of wiring lines and the plurality ofresistance heating elements may be coupled to each other by connectors.

In the present disclosure, both end portions of at least either one ofthe pair of wiring lines may be coupled by a coupling means.

In addition, the present disclosure is a heating device for a vacuumpump that includes the heating means in the above-mentioned vacuum pump.

According to the present disclosure, specific configurations of thevacuum pump and the heating device therefor adopt the configuration inwhich the heating means includes the plurality of resistance heatingelements connected in parallel to the pair of wiring lines, as describedabove. Therefore, even if, for example, any one of the plurality ofresistance heating elements breaks down, the rest of the heatingresistance elements can be operated normally, and the exhaust flow pathcan constantly be heated by these normal resistance heating elements.Accordingly, owing to the fact that deposition of products in theexhaust flow path can be prevented by such continuous heating, thepresent disclosure can realize a vacuum pump and a heating devicetherefor that are suitable for prolonging the life of the heating meansused as a measure to prevent product deposition in the vacuum pump.

According to the present disclosure, even if, for example, any one ofthe resistance heating elements breaks down, the exhaust flow path canconstantly be heated, preventing deposition of products in the exhaustflow path, as described above. Therefore, the present disclosure alsohas the advantage that the operation of a device to be vacuumed by thevacuum pump of the present disclosure, that is, for example, a processapparatus in a semiconductor manufacturing apparatus, can be continued.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a vacuum pump to which the presentdisclosure is applied.

FIG. 2 is a block diagram including an electric circuit configuration ofa heating means of the present disclosure.

FIG. 3 is a component arrangement diagram of the electric circuitconfiguration shown in FIG. 2.

FIG. 4 is a component arrangement diagram of the electric circuitconfiguration shown in FIG. 2.

FIG. 5 is a flowchart showing operation control steps performed on thevacuum pump by a pump control means.

FIG. 6 is an explanatory diagram of an electric circuit configuration ofthe heating means adopted by the conventional vacuum pump.

DETAILED DESCRIPTION

The best mode for carrying out the present disclosure is now describedhereinafter in detail with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view of a vacuum pump to which the presentdisclosure is applied. FIG. 2 is a block diagram including an electriccircuit configuration of a heating means of the present disclosure.FIGS. 3 and 4 are each a component arrangement diagram of the electriccircuit configuration shown in FIG. 2.

As shown in FIG. 1, a vacuum pump P1 shown in the diagram includes acasing 1 having a cylindrical cross-sectional shape, a rotating body RBdisposed inside the casing 1, a support means for rotatably supportingthe rotating body RB, and a drive means for driving the rotating body RBto rotate.

The casing 1 has a bottomed cylindrical shape in which a cylindricalpump case 1A and a bottomed cylindrical pump base 1B are integrallycoupled to each other in a cylinder axis direction thereof by fasteningbolts. An upper end of the pump case 1A is opened as an inlet port 2 forsucking gas, and a side surface of a lower end of the pump base 1B isprovided with an outlet port 3 for exhausting the gas to the outside ofthe casing 1.

The inlet port 2 is connected to a vacuum chamber (not shown) that is ina high vacuum, such as a process chamber constituting a processapparatus of a semiconductor manufacturing apparatus, via a pressureadjustment valve which is not shown. The outlet port 3 is connected in acommunicating manner to an auxiliary pump, not shown.

A cylindrical stator column 4 having various electrical componentsstored therein is provided in the center of the pump case 1A. In thevacuum pump P1 of FIG. 1, the stator column 4 is formed as a separatecomponent from the pump base 1B and fixed to an inner bottom of the pumpbase 1B by screws, whereby the stator column 4 is provided upright onthe pump base 1B. However, in another embodiment, the stator column 4may be provided upright integrally on the inner bottom of the pump base1B.

Inside the pump base 1B are a pair of wiring lines WL1, WL2 (see FIG. 2)and a plurality of resistance heating elements RE (see FIG. 2) providedas components constituting a heating means HM (see FIG. 2). A detailedconfiguration of the heating means HM is described hereinafter. Notethat the place for installing the components constituting the heatingmeans HM is not limited to the pump base 1B and can be changed asneeded.

A rotor 6 constituting the rotating body RB is provided outside thestator column 4. The rotor 6 is enclosed in the pump case 1A and thepump base 1B and has a cylindrical shape so as to surround an outerperiphery of the stator column 4.

A rotor shaft 5 is provided inside the stator column 4 as a rotationcentral axis of the rotating body RB. The rotor shaft 5 is disposed insuch a manner that an upper end thereof faces the inlet port 2 and alower end thereof faces the pump base 1B. The rotor shaft 5 is rotatablysupported by a magnetic bearing (specifically, two pairs of known radialmagnetic bearings MB1 and a pair of known axial magnetic bearings MB2).Furthermore, a drive motor MO is provided inside the stator column 4,and the rotor shaft 5 is driven to rotate about the axis thereof by thisdrive motor MO.

The upper end of the rotor shaft 5 protrudes upward from a cylindricalupper end surface of the stator column 4, and an upper end of the rotor6 is integrally fixed to this protruding upper end of the rotor shaft 5by a fastening means such as bolts. The rotor 6, therefore, is rotatablysupported by the magnetic bearings (the radial magnetic bearings MB1,the axial magnetic bearings MB2) via the rotor shaft 5, and when thedrive motor MO is started in this supported state, the rotor 6 canrotate integrally with the rotor shaft 5 around its rotor axis.

In other words, in the vacuum pump P1 shown in FIG. 1, the magneticbearings function as a support means for rotatably supporting the rotorshaft 5 and the rotor 6, and the drive motor MO functions as a drivemeans for drive the rotor 6 to rotate.

The vacuum pump P1 shown in FIG. 1 also includes, between the inlet port2 and the outlet port 3, a plurality of exhaust steps PT that functionas a means for exhausting gas molecules.

Also in the vacuum pump P1 shown in FIG. 1, a thread groove pump step PSis provided downstream of the plurality of exhaust steps PT, i.e.,between the bottom exhaust step PT (PTn) of the plurality of exhauststeps PT and the outlet port 3.

Detailed Configuration of Plurality of Exhaust Steps PT

The upstream side of the vacuum pump P1 of FIG. 1 from substantially themiddle of the rotor 6 functions as the plurality of exhaust steps PT.The plurality of exhaust steps PT are described hereinafter in detail.

A plurality of rotor blades 7 rotating integrally with the rotor 6 areprovided on an outer peripheral surface of the rotor 6 that is upstreamfrom substantially the middle of the rotor 6, and these rotor blades 7are arranged radially at predetermined intervals around a rotationcentral axis of the rotor 6 (specifically, the axis of the rotor shaft5) or an axis of the casing 1 (referred to as “vacuum pump axis”,hereinafter), for the respective exhaust steps PT (PT1, PT2, PTn).

Meanwhile, on the inner peripheral side of the pump case 1A, a pluralityof stator blades 8 are provided, and these stator blades 8 are arrangedradially at predetermined intervals around the vacuum pump axis, for therespective exhaust steps PT (PT1, PT2, . . . PTn), as with the rotorblades 7.

Specifically, the vacuum pump P1 shown in FIG. 1 has a structure inwhich the multiple exhaust steps PT (PT1, PT2, . . . PTn) are providedbetween the inlet port 2 and the outlet port 3 and the plurality ofrotor blades 7 and stator blades 8 are arranged radially atpredetermined intervals for the respective exhaust steps PT (PT1, PT2, .. . PTn), thereby exhausting the gas molecules.

Each of the rotor blades 7 is a blade-like cut product that is formed,by cutting, integrally with an outer diameter treated portion of therotor 6, and is inclined at an angle appropriate for exhausting the gasmolecules. Each of the stator blades 8 is also inclined at an angleappropriate for exhausting the gas molecules.

Explanation of Exhaust Operation Performed by Plurality of Exhaust StepsPT

Of the plurality of exhaust steps PT configured as described above, atthe top exhaust step PT (PT1), the plurality of rotor blades 7 rotatesat a high speed integrally with the rotor shaft 5 and the rotor 6 whenthe drive motor MO is activated. Such rotating rotor blades 7 provides adownward, tangential momentum to the gas molecules that have enteredfrom the inlet port 2, by an inclined surface of each rotor blade 7,which is tilted forward and downward (the direction from the inlet port2 to the outlet port 3, referred to as “downward”, hereinafter) in thedirection of rotation of the rotor blades 7. The gas molecules with thisdownward momentum are sent to the next exhaust step PT (PT2) provided onthe corresponding stator blade 8, by the opposite downward inclinedsurface in the direction of rotation of the rotor blades 7. Further, aswith the top exhaust step PT (PT1), at the next exhaust step PT (PT2)and the subsequent exhaust steps PT as well, the momentum is applied tothe gas molecules by rotation of the rotor blades 7 and the gasmolecules are sent by the stator blades 8, as described above. In thismanner, the gas molecules in the vicinity of the inlet port 2 aresequentially shifted and exhausted toward the downstream side of therotor 6.

Detailed Configuration of Thread Groove Pump Step PS

The downstream side of the vacuum pump P1 of FIG. 1 from substantiallythe middle of the rotor 6 functions as the thread groove pump step PS.The thread groove pump step PS is described hereinafter in detail.

The thread groove pump step PS includes a thread groove stator 9 as ameans for forming a thread groove-like exhaust flow path R at the outerperipheral side of the rotor 6 (specifically, at the outer peripheralside of the downstream part of the rotor 6 from substantially the middleof the rotor 6), and this thread groove stator 9 is attached to an innerperiphery of the casing 1 as a stator member.

The thread groove stator 9 is a cylindrical stator member that isdisposed in such a manner that an inner peripheral surface thereof facesthe outer peripheral surface of the rotor 6. The thread groove stator 9is also disposed so as to surround the downstream part of the rotor 6from substantially the middle of the rotor 6.

The downstream part of the rotor 6 from substantially the middle of therotor 6 is a part where the thread groove pump step PS rotates as arotating member, and is inserted/stored in the thread groove stator 9,with a predetermined gap therebetween.

A thread groove 91 in a tapered shape, the depth of which decreasestoward the bottom, is formed in an inner peripheral portion of thethread groove stator 9. The thread groove 91 is formed in a spiral shapefrom an upper end to a lower end of the thread groove stator 9.

The exhaust flow path R for exhausting the gas is formed on the outerperipheral side of the rotor 6 by the thread groove stator 9 having thethread groove 91 described above. Although not shown, the exhaust flowpath R described above may be provided by forming the thread groove 91described above in the outer peripheral surface of the rotor 6.

In the thread groove pump step PS, since the gas is compressed andtransferred by the thread groove 91 and the drag effect on the outerperipheral surface of the rotor 6, the depth of the thread groove 91 isset to be the deepest at the upstream entrance side (a flow path openingend in the vicinity of the inlet port 2) of the exhaust flow path R andthe shallowest at the downstream exit side (a flow path opening end inthe vicinity of the outlet port 3).

The entrance of the exhaust flow path R (the upstream open end) isopened toward a gap between a stator blade 8 n constituting the bottomexhaust step PTn and the thread groove stator 9 (referred to as “finalgap GE”, hereinafter), whereas the exit of the exhaust flow path R (thedownstream open end) is communicated with the outlet port 3 through anin-pump outlet port side flow path PR.

By providing a predetermined gap between the lower end of the rotor 6 orthe thread groove stator 9 and the inner bottom portion of the pump base1B (a gap going once circle around a lower outer periphery of the statorcolumn 4, in the vacuum pump P1 shown in FIG. 1), the in-pump outletport side flow path PR is formed so as to extend from the exit of theexhaust flow path R to the outlet port 3.

Explanation of Exhaust Operation of Thread Groove Pump Step PS

The gas molecules that reach the final gap GE by being transferred bythe exhaust operation by the plurality of exhaust steps PT describedabove are transferred to the exhaust flow path R of the thread groovepump step PS. The transferred gas molecules move toward the in-pumpoutlet port side flow path PR while being compressed from thetransitional flow to the viscous flow by the drag effect generated bythe rotation of the rotor 6. The gas molecules that reach the in-pumpoutlet port side flow path PR flow into the outlet port 3 and areexhausted to the outside of the casing 1 through the auxiliary pumpwhich is not shown.

Detailed Configuration of Heating Means HM

Referring to FIGS. 2 and 3, the heating means HM has an electric circuitconfiguration in which the plurality of (six, specifically) resistanceheating elements RE are connected in parallel to the pair of wiringlines WL1, WL2. Moreover, a thermostat is incorporated as an overheatprevention means 104 in this electric circuit configuration, and theposition to incorporate the thermostat can be changed as needed.

The pair of wiring lines WL1, WL2 are arranged in such a manner as tosurround an outer periphery of the rotating body RB inside the pump base1B. The wiring line WL1 is connected to a power supply (ACC), not shown,whereas the wiring line WL2 is connected to the ground (GND).

The plurality of resistance heating elements RE are arranged radially atequal intervals around the rotating body RB inside the pump base 1B, andgenerate heat by being electrically energized, to intensively heat thevicinity of the exit of the exhaust flow path R in the thread groovepump step PS via the pump base 1B.

In the vacuum pump P1 shown in FIG. 1, the plurality of resistanceheating elements RE are installed inside the pump base 1B due to thefact that the pressure is high in the vicinity of the exit of theexhaust flow path R and products are most likely to accumulate therein,and that the pump base 1B is located in the vicinity of the exit of theexhaust flow path R. However, the present disclosure is not limited tothis installation example.

For example, the plurality of resistance heating elements RE may beinstalled inside the thread groove stator 9, or the plurality ofresistance heating elements RE may be installed in a vacuum pump statormember other than the pump base 1B or thread groove stator 9.

In addition, the number of resistance heating elements RE is not limitedto six and therefore can be increased or decreased as needed. The vacuumpump P1 shown in FIG. 1 adopts a structure in which, for the purpose ofimproving the maintainability of the heating means HM such as replacinga faulty resistance heating element RE with a new one, the pair ofwiring lines WL1, WL2 and the plurality of resistance heating elementsRE are coupled by connectors CT (referred to as “connector coupling”,hereinafter) so that the wiring lines WL1, WL2 and the plurality ofresistance heating elements RE can each be attached and detached.

The vacuum pump P1 can also adopt a structure in which the pair ofwiring lines WL1, WL2 and the plurality of resistance heating elementsRE are directly connected without using the connectors CT (referred toas “direct connection structure”, hereinafter). However, according tosuch a direct connection structure, in a case where a faulty resistanceheating element RE is found using, for example, a current detectionmeans which is prepared separately, and this faulty resistance heatingelement RE needs to be replaced with a new one, the entire heatingcircuit constituted by all the resistance heating elements RE and thepair of wiring lines WL1, WL2 needs to be removed. In this regard, thedirect connection structure may not bring about good maintainability ofthe heating means HM.

The connector coupling described above, on the other hand, can bringabout excellent maintainability of the heating means HM due to the factthat only the faulty resistance heating element RE can be removed fromthe pair of wiring lines WL1, WL2 by disconnecting the connectors CT.

In the vacuum pump P1 shown in FIG. 1, both end portions of therespective wiring lines WL1, WL2 are not coupled to each other. Inanother embodiment, however, both end portions of at least either one ofthe wiring lines (either WL1 or WL2) may be coupled by a coupling meansCP as in the example shown in FIG. 4.

In this case, as the coupling means CP, the both end portions of thewiring line WL1 (or WL2) may be electrically conducted by adopting, forexample, known connectors used for connecting electric wires.Alternatively, the both end portions of the wiring line WL1 (or WL2) maynot be electrically conducted by adopting, as the coupling means CP, acoupling component other than the known connectors, such as hooks andrings that can be engaged with the hooks.

An advantage of the configuration adopting the coupling means CPdescribed above is that fixing the end portions of the wiring lines WL1,WL2 by using the coupling means CP makes handling of the wiring linesWL1, WL2 easy when the wiring lines WL1, WL2 are arranged so as tosurround the outer periphery of the rotating body RB inside the pumpbase 1B, improving the arrangement and workability of the wiring lines.

Referring to FIG. 2, the heating means HM is composed of the pluralityof resistance heating elements RE and may include a current measuringmeans 101 for measuring the sum of values of flowing currents, adetermination means 102 for determining the failure conditions of theplurality of resistance heating elements RE on the basis of the measuredvalue obtained by the current measuring means 101 (referred to as a“failure condition determination means 102”, hereinafter), and an outputmeans 103 for outputting the failure conditions determined by thefailure condition determination means 102 (referred to as a “failurecondition output means 103”, hereinafter).

A known current measuring device can be used as the current measuringmeans 101. Although in the example shown in FIG. 2, the currentmeasuring means (current measuring device) is installed in the wiringline WL2 in order to measure the sum of the values of the currentsflowing through the plurality of resistance heating elements RE, thepresent disclosure is not limited to this installation example; thecurrent measuring means 101 may be installed on the wiring line WL1.

Note that, in the present embodiment, the operation of the vacuum pumpP1 in a state in which all of the plurality of resistance heatingelements RE are operated normally (state without failure) is referred toas “normal operation of the vacuum pump P1”, and a current value Ipmeasured by the current measuring means during this normal operation ofthe vacuum pump P1 is referred to as “normal operation total currentvalue Ip”.

The failure condition determination means 102 determines “the number offaulty resistance heating elements RE” as an example of the failureconditions. This process for obtaining the number of faulty resistanceheating elements RE is described hereinafter in “Process for obtainingcurrent reduction rate X and the number S”. The failure condition outputmeans 103 outputs the failure conditions (the number of faultyresistance heating elements RE) determined by the failure conditiondetermination means 102 to, for example, a control means CM of thevacuum pump P1.

Control Means of Vacuum Pump P1

The control means CM of the vacuum pump P1 (referred to as a “pumpcontrol means CM”, hereinafter) controls the operation of the vacuumpump P1 in an integrated manner, and includes various drive circuits DRfor driving pump electrical components such as the radial magneticbearings MB1, the axial magnetic bearings MB2, and the drive motor MOdescribed above, a CPU for outputting operation start/stop commands tothe various drive circuits DR, and a data storage unit ME including aROM, a RAM, a hard disk, and the like.

Moreover, the pump control means CM controls the operation of the vacuumpump P1 by performing not only various determination processes such asdetermining whether the resistance heating elements RE need to bemaintained or not, based on the failure conditions (the number of faultyresistance heating elements RE) output from the failure condition outputmeans 103, but also immediately stopping the operation of the vacuumpump P1 when it is determined that the resistance heating elements REneed to be maintained. In order to perform such control, the normaloperation total current value Ip that is described above is stored andrecorded in advance in the data storage unit ME of the pump controlmeans CM.

The normal operation total current value Ip may be recorded prior toshipment, or an actual total current value during normal operation ofthe heating means HM that is obtained immediately after the start of theoperation of the vacuum pump P1 may be recorded as the normal operationtotal current value Ip.

Explanation of Control Operation of Vacuum Pump P1

FIG. 5 is a flowchart showing operation control steps performed on thevacuum pump by the pump control means CM.

A series of operation control steps shown in the flowchart in FIG. 5 istriggered by, for example, the start of the operation of the vacuum pumpP1, and, first, the normal operation total current value Ip is read fromthe data storage unit ME of the pump control means CM (ST1), then thesum of the values of the currents actually flowing through the pluralityof resistance heating elements RE (referred to as “actual total currentvalue Ip′”, hereinafter) is measured by the current measuring means 101(ST2), and thereafter the normal operation total current value Ip andthe actual total current value Ip′ are compared with each other (ST3).

As a result of the comparison in ST3 described above, when the normaloperation total current value Ip is equal to the actual total currentvalue Ip′, the heating means HM continues to heat the exhaust flow pathR by keeping the electrical conduction of the plurality of resistanceheating elements RE and causing the plurality of resistance heatingelements RE to generate heat (Yes in ST3, ST4).

Subsequently, information contributing to impeding the normal operationof the vacuum pump P1, such as a decrease in the internal temperature ofthe vacuum pump P1 or an increase in the amount of vibration due to therotating body RB being unbalanced, is collected by various accompanyingsensors of the vacuum pump P1, which are not shown, and on the basis ofthe collected information, it is determined whether the vacuum pump P1needs to be maintained or not (referred to as “pump maintenancedetermination”, hereinafter) (ST5).

When it is determined in the pump maintenance determination of ST5described above that “the vacuum pump P1 does not need to bemaintained”, the process returns to ST2 (No in ST5), but when it isdetermined that “the vacuum pump P1 needs to be maintained”, theoperation of the vacuum pump P1 is stopped (ST6).

As a result of the comparison in ST3 described above, when the normaloperation total current value Ip is not equal to the actual totalcurrent value Ip′, a process for determining the conditions of theresistance heating elements RE of the heating means HM (the number offaulty resistance heating elements RE) is performed (referred to as“heater condition determination process”, hereinafter) (ST7). Then, onthe basis of the conditions of the resistance heating elements REdetermined in ST7 (the number of faulty resistance heating elements RE),a process for determining whether the resistance heating elements REneed to be maintained or not (referred to as “heater maintenancedetermination process”, hereinafter) is performed (ST8).

When it is determined in ST8 described above that “the heatermaintenance is not necessary”, the process shifts to ST4 (No in ST8),but when it is determined that “the heater maintenance is necessary”,the operation of the vacuum pump P1 is stopped (ST6).

Details of Heater Condition Determination Process of ST7

The heater condition determination process of ST7 calculates the currentreduction rate X (ST71) and obtains the number S (integer) of faultyresistance heating elements RE on the basis of the calculated currentreduction rate X (ST72). This process for calculating the currentreduction rate X and the process for obtaining the number S of faultyresistance heating elements RE are described hereinafter in “process forobtaining the current reduction rate X and the number S”.

Process for Obtaining Current Reduction Rate X, Number S

Assuming that the current reduction rate is X, the current reductionrate X can be determined by the following expression (1).

X=(Ip−Ip′)/Ip   Ex. (1)

Also, assuming that the number of faulty resistance heating elements REis S (integer) and the total number of resistance heating elements RE isN, the number S (integer) is obtained by the following expression (2) onthe basis of the current reduction rate X.

(S−1)/N<X≤S/N   Ex. (2)

The following expression (3) is obtained by modifying the right side ofthe expression (2).

N·X<S   Ex. (3)

The following expression (4) is obtained by modifying the left side ofthe expression (2).

S<N·X+1   Ex. (4)

The number S of faulty resistance heating elements RE satisfies theconditions of the expressions (3) and (4), i.e., the condition of thefollowing expression (5).

N X≤S<N·X+1   Ex. (5)

Here, for example, assuming that the total number N of resistanceheating elements RE is 10, that the normal operation total current valueIp is 10 amperes, and that the actual total current value Ip′ is 8.2amperes, the current reduction rate X (=(Ip−Ip′)/Ip) is 0.18(=(10−8.2)/10=0.18). By substituting this current reduction rate X(=0.18) and the total number N of resistance heating elements RE (=10)into the expression (5), the expression (5) becomes the followingexpression (6). The expression (6) below can determine that the number S(integer) of faulty resistance heating elements RE is two.

1.8≤S<2.8   Ex. (6)

Details of Heater Maintenance Determination Process of ST8

The heater maintenance determination process of ST8 calculates thefailure rate of the resistance heating elements RE (=the number S offaulty resistance heating elements/the total number N of resistanceheating elements), and determines that “the heater maintenance isnecessary” when the calculated failure rate is greater than a referencefailure rate that is set in advance (referred to as “reference failurerate”, hereinafter) or determines that “the heater maintenance is notnecessary” in other situations (ST8).

For example, when it is assumed that the operation of the vacuum pump P1has no problem as long as 80% or more of the total number of resistanceheating elements RE are operated normally, and when the condition of thefollowing expression (7) is satisfied on the assumption that thereference failure rate is 0.2, it may be determined that “the heatermaintenance is necessary”, and an alarm for urging the maintenance isoutput to issue a maintenance request warning (ST8).

0.2<S/N   Ex. (7)

S: The number of faulty resistance heating elements

N: Total number of resistance heating elements

Stopping Vacuum Pump P1 in ST6

When stopping the vacuum pump P1 in ST6, for example, the pump controlmeans CM performs processes necessary for stopping the operation of thevacuum pump P1, such as outputting an operation stop command from theCPU of the pump control means CM to various drive circuits for drivingthe pump electrical components such as the radial magnetic bearings MB1,the axial magnetic bearings MB2, and the drive motor MO (ST6).

According to the vacuum pump P1 of the present embodiment describedabove, as a specific configuration, the heating means HM adopts theelectric circuit configuration in which the plurality of resistanceheating elements RE are connected in parallel to the pair of wiringlines WL1, WL2. Therefore, even if any one of the plurality ofresistance heating elements RE breaks down, the rest of the heatingresistance elements can be operated normally and the exhaust flow path Rcan constantly be heated by these normal resistance heating elements.Accordingly, owing to the fact that deposition of products in theexhaust flow path R can be prevented by such continuous heating, thepresent disclosure is suitable for prolonging the life of the heatingmeans HM used as a measure to prevent product deposition in the vacuumpump P1.

Furthermore, according to the vacuum pump P1 of the present embodiment,even if, for example, any one of the resistance heating elements breaksdown, the exhaust flow path R can constantly be heated, preventingdeposition of products in the exhaust flow path R, as described above.Therefore, the present disclosure also has the advantage that theoperation of a device to be vacuumed by the vacuum pump P1, that is, forexample, a process apparatus in a semiconductor manufacturing apparatus,can be continued.

The heating means HM constituting the vacuum pump P1 of the presentembodiment described above may be configured as a heating deviceseparate from the vacuum pump P1

The present disclosure is not limited to the embodiments describedabove, and many modifications can be made by those having ordinaryknowledge in the art within the technical

REFERENCE SIGNS LIST

-   1 Casing-   1A Pump case-   1B Pump base-   2 Inlet port-   3 Outlet port-   4 Stator Column-   5 Rotor shaft-   6 Rotor-   7 Rotor blade-   8 Stator blade-   9 Thread groove stator-   91 Thread groove-   101 Current measuring means-   102 Determination means (failure condition determination means)-   103 Output means (failure condition output means)-   104 Overheat prevention means-   CM Control means (pump control means)-   CP Coupling means-   CT Connector-   DR Various drive circuits-   GE Final gap-   HM Heating means-   MB1 Radial magnetic bearing-   MB2 Axial magnetic bearing-   ME Data storage unit-   MO Drive motor-   P1 Vacuum pump-   PS Thread groove pump step-   RB Rotating body-   PT Exhaust step-   PT1 Top exhaust step-   PTn Bottom exhaust step-   PR In-pump outlet port side flow path-   R Exhaust flow path-   RE Resistance heating element-   WL1, WL2 Wiring lines

1. A vacuum pump that exhausts gas by rotation of a rotating body, thevacuum pump comprising: an exhaust flow path for exhausting the gas; anda heating means for heating the exhaust flow path, wherein the heatingmeans includes a plurality of resistance heating elements connected inparallel to a pair of wiring lines.
 2. The vacuum pump according toclaim 1, further comprising: a current measuring means for measuring asum of values of currents flowing through the plurality of resistanceheating elements; and a determination means for determining failureconditions of the plurality of resistance heating elements on the basisof a measured value obtained by the current measuring means.
 3. Thevacuum pump according to claim 2, further comprising: an output meansfor outputting the failure conditions determined by the determinationmeans.
 4. The vacuum pump according to claim 2, wherein the failureconditions are a number of faulty resistance heating elements out of theplurality of resistance heating elements.
 5. The vacuum pump accordingto claim 1, wherein the pair of wiring lines and the plurality ofresistance heating elements are coupled to each other by a connector. 6.The vacuum pump according to claim 1, wherein both end portions of atleast either one of the pair of wiring lines are coupled by a couplingmeans.
 7. A heating device for a vacuum pump that includes the heatingmeans in the vacuum pump according to claim 1.